An application IC that can be applied in the control system of a memory storage device for the USB device for communicating with a server for receiving, reading and writing commands from the server and to access to the data stored in various memory storage devices is provided. Alternatively, the application IC can support the server, including IDE portable information product for data transmission. The data transmission having these two different specifications can share the same data source in certain mechanism. In this mechanism, the USB server is in the first priority transfer mode, the IDE server will take action only when the USB server is unavailable or discharged. When the IDE server is in operation mode, the interruption demand from the USB server is denied and after the IDE server completes the assignment, the interruption command from the USB server is executed.